Heat exchangers have long been used for many purposes. In more recent years, two-phase heat exchangers have been used to achieve high heat transfer rates, exploiting the fact that the latent heat of evaporation is generally much higher than the sensible heat required to increase the temperature of the same mass of fluid over a given temperature differential. That fact allows two-phase heat exchangers to transfer thermal energy more rapidly across the same area for a similar temperature gradient, ΔT, than can be achieved with a one-phase heat transfer system. Two-phase heat transfer technology generally is well known to those skilled in the art and is well described in the literature. The transfer of heat by heat exchangers is also well known, and many well-recognized texts address the design and engineering of heat transfer and heat exchanger mechanisms.
There is a well recognized need for new technologies that permit rapid thermal cycling of materials, devices, and other systems. The present invention discloses a novel way of using two-phase heat transfer to rapidly input heat to, and remove heat from, systems in general so that rapid thermal cycling of the system occurs over a desired temperature range. Thermal cycling is achieved by varying the pressure of a working fluid in a chamber so that some portion of the fluid rapidly cycles back and forth between liquid and gas phases. As condensation and evaporation alternately occur during those phase changes, large amounts of latent heat are expelled and absorbed by the fluid, respectively. That large amount of latent heat expelled and absorbed by the fluid, in turn, is used to input and remove heat from the desired system, respectively. Rapid thermal cycling of the system is achieved thereby.
Thermal cycling with the invention can be used in a wide range of applications. One such application is for the generation of electricity from thermal energy using ferroelectrics or other electrically polarizable materials. Apparatus and methods for using the inherent spontaneous polarization of ferroelectrics and polarizable amorphous polymers, and the rapid change in such polarization that occurs with temperature cycling, are disclosed, for example, in the U.S. patents and patent applications referenced above. More rapid thermal cycling with the present two-phase invention allows for more effective use of those materials and devices. In the case of power generation, for example, the specific power of the material may increase in proportion to the square of the cycling speed under some circumstances. There are other applications where rapid thermal cycling is desirable, and the invention can generally be used with such applications to achieve more effective cycling and more robust thermal transfer. It is also expected that additional applications will be developed in the future that require or benefit from rapid thermal cycling, and the invention will be useful with those applications as well.